Adrian wrote:

Is the metal protrusion on the left just a poorly-punched-out hole - or
is it there a reason ? (before I take a hammer to it!)

Unless it's got a really clever purpose, I'd imagine it's going to
affect 'inside' measurements....

http://www.inspired-glass.com/html/uk-diy.html

I have a similar one, with a magnetic tip - is yours magnetic too?

Daniele